Monitoring of sterilization parameters is essential to ensure that optimum sterilizing conditions during a steam or chemical sterilization cycle are met. Environmental conditions in the chamber are frequently measured by various sensors, such as temperature, pressure, or sterilant concentration sensors, positioned in strategic places, such as a chamber wall or a drain line. The sensors, in turn, may be connected by various methods (e.g. electrical, radio transmitter, etc.) to an integral or remote microprocessor controller programmed to monitor and respond to the sensor readings and provide control of critical cycle parameters in the chamber, such as temperature, pressure, relative humidity, sterilant concentration and time during the cycle.
Control of cycle parameters in the chamber, however, does not guarantee that sterilization conditions have been met within the load to be sterilized. Systems have been developed employing temperature and pressure sensors placed within an actual load or in standardized devices simulating a load. Each of these prior systems has disadvantages. For example, a sensor placed in an actual load monitors a condition only at the sensor location and does not necessarily reflect the condition elsewhere in the load. Load simulation devices, such as those containing a heat sink to detect the presence of air or superheated steam or those containing sensors to monitor and record time, temperature pressure and/or moisture, have the disadvantage that the load-simulation devices are not integrated with the sterilizer control system and are monitors only. In some, information is available only after the sterilization cycle, when the device is removed from the chamber and the record of a parameter is interpreted visually (e.g. a color change) by the operator. In others, the monitored information is transmitted to an external stand alone control and display unit, adding to the expense of a sterilization system. Neither approach provides the capability of real-time monitoring of critical load parameters with direct and simultaneous conveyance of the information to the sterilizer control system allowing real-time control of critical sterilization parameter levels within the load. Further, prior load-simulation devices monitor only such parameters as temperature, pressure, time, moisture or the presence of a sterilant. They do not provide the capability of also directly monitoring the concentration of a chemical sterilant, such as ethylene oxide gas or hydrogen peroxide liquid or vapor, in a load, or of directly conveying the results to the sterilization control for real-time control of the sterilant concentration in the load.
Currently, the Association for Advancement of Medical Instrumentation (AAMI) guidelines recommend that chemical integrators and biological indicators be used to verify that process parameters critical for sterilization have been achieved. Chemical integrators provide a visual indication (e.g. a color change) that predetermined sterilization parameters were presumably achieved. For example, in the case of steam or ethylene oxide sterilization, a chemical integrator might indicate that a given temperature with the presence of moisture was achieved for a given time. Chemical integrators, however, are not sophisticated enough to monitor critical cycle parameters (e.g. temperature, pressure, sterilant concentration) to a confidence level that would assure that sterilization has occurred and to allow release of the load for use based on the indicator results alone. Therefore, biological indicators are additionally employed. Presumably, if proper conditions in the chamber with respect to time, temperature, pressure and/or sterilant concentration are achieved and maintained for the required exposure period, the biological agent in the indicator will be killed, and thereby indicate cycle efficacy. However, the requirement for a sometimes lengthy incubation of the biological indicator to assure confirmation of sterility can result in an undesirable time delay after cycle completion before the sterilization efficacy is known. This delay can significantly affect productivity and, therefore, the cost of processing goods through the sterilization system, in addition to the inconvenience of delayed turnaround of critical medical or dental instruments.
Recently, the concept of parametric release has been described for moist heat sterilization, and seeks to provide a more efficient means for monitoring a steam sterilization process. Parametric release is based on the physical monitoring in the chamber of the parameters of pressure, temperature and rate of change of temperature and pressure during the moist heat sterilization cycle. The chamber control is set for a predetermined cycle, to achieve and maintain predetermined critical parameter levels for a given period of time. The chamber parameters are monitored throughout the cycle. If the monitoring indicates a difference between a set and measured parameter value that exceeds specified limits, a warning is given to the cycle operator. If the monitoring indicates that the critical levels in the chamber are achieved and maintained for the time required to achieve a given sterility assurance level, the cycle is considered efficacious and the load is released for use. Therefore, parametric release systems are designed to provide monitoring and notification only of achieved parameters in the chamber. They do not suggest providing real-time sensing data to the sterilizer control system to enable the sterilizer control to react to changes in the critical parameters and adjust them in order to avoid unsuccessful cycles. Rather, current International Organization For Standardization (ISO) and European Committee for Standardization (CEN) standards require that the monitoring system for parametric release be separate from the sterilizer control system. Further, the process is described only for control of parameters in the chamber and does not address the monitoring and control of the critical parameter levels in the load itself.
A need exists, therefore, for a sterilization system that provides both real-time monitoring and real-time control of critical sterilization parameters in the load, to a sterility assurance level that eliminates the need for chemical and biological indicators. Moreover, there is a need for a device that provides real-time monitoring of critical sterilization parameters in the load, and is also integrated with the sterilizer control system to enable the control to react to monitored changes in the critical parameter levels and adjust them in real-time in order to avoid unsuccessful cycles. Additionally, there is a need for a device that reproducibly simulates a standard challenge load undergoing sterilization and that contains critical parameter sensors that are directly integrated into the sterilizer control system. Furthermore, there is a need for a sterilization system that provides for the release of a load when the critical values of sterilization parameters in the load are shown to have been met.